The present invention relates to an apparatus for detecting the failure of one or more wires of an electrical system. More particularly, the present invention is directed to an apparatus for detecting damage to or breakage of one or more return wires of an electrical instrument and for deactivating the delivery of energy to the electrical instrument upon the detection of damage.
The use of electrical instruments in the diagnosis and treatment of a variety of medical conditions is now commonplace. However, the use of such electrical equipment in direct contact with the body can pose significant risks to the patient in the event that there is an electrical malfunction in the instrument. For example, a patient can be subjected to electrical shocks or burns if the electrical instrument malfunctions while in contact with the human body. Additional harm may be incurred by the patient due to involuntary neuromuscular responses to electrical energy inadvertently directed to the body.
Electrical medical instruments can malfunction for a variety of reasons, including, but not limited to, damage to and breakage of wires within the instrument caused by repeated sterilization cycles which subject the wires to significant wear. For this reason, efforts have been made to develop technologies capable of reducing the risk of harming a patient in the event of an electrical malfunction as well as technology capable of detecting malfunctions within the electrical equipment.
Electrical medical instruments typically include an active electrical wire that delivers electrical energy to an electrically operated device and a return wire that allows electrical current to return to the power source from the electrically operated device. One example of an electrical medical instrument of this type is a phacoemulsification handpiece which includes an active electrical wire that delivers electrical energy from an electrical power source to a transducer which generates vibratory energy in response to the electrical energy. This vibratory energy is imparted to a phacoemulsification needle which is used to break up and remove a cataractous lens from the eye of a patient. Electrical current from the transducer is returned to the electrical power source through one or more return electrical wires.
A patient undergoing treatment with an electrical medical instrument is exposed to relatively little risk in the event that the active electrical wire breaks during use because electrical energy will not be delivered to the electrically operated device when the active electrical wire is broken. This mode of failure is also readily recognized by the medical specialist using the electrical medical instrument because the instrument will not operate when the active electrical wire is broken.
No such comfort level exists in the event that one or more of the return wires is damaged or broken due to the fact that the electrical medical instrument may continue to operate despite the malfunction. Thus, the medical specialist has no clear indication that the instrument has malfunctioned, although in certain cases an electrical shock may be delivered to the medical specialist when using the malfunctioning instrument. In addition, such a malfunction will simultaneously subject the patient to a significant risk of exposure to electrical energy and the injuries associated therewith due to the fact that the patient's body will become an alternative ground path for the electrical medical instrument.
In order to reduce the risks associated with the damage or breakage of a return electrical wire, some electrical medical instruments employ two or more return electrical wires, thereby providing multiple pathways through which electrical current can pass after leaving the electrically operated device and thereby reducing the likelihood that electrical energy will be delivered to the patient when only one of the return electrical wires is damaged or breaks. Although devices of this type may reduce the incidence of inadvertent delivery of electrical energy to a patient, they do not eliminate the problem at hand. Such devices do not provide any indication to the medical specialist that one or more of the return electrical wires is damaged or broken, nor do they prevent the delivery of electrical energy to the patient in the event that all of the return electrical wires are damaged or broken.
An alternative mechanism for reducing the risk of inadvertent delivery of electrical energy to a patient is disclosed in U.S. Pat. No. 4,793,345 to Lehmer. The Lehmer device employs two return electrical wires and monitors the respective current levels in each of the return wires through the use of a transformer core. When there is a current imbalance between the return wires caused by damage or breakage to one of the wires, a signal can be generated indicating that a current imbalance exists. However, it will be appreciated the Lehmer device fails to address the situation in which both of the return wires break simultaneously insofar as the current levels in both of the wires will be zero, i.e., balanced.
Another example of an apparatus for preventing the delivery of electrical energy to a patient is disclosed in U.S. Pat. No. 4,437,464 to Crow which is incorporated herein by reference. Crow discloses the use of a transformer core through which both an active electrical wire and a return electrical wire pass. The active and return electrical wires are wound about the transformer core in opposite directions such that only a minimal impedance is created by the transformer core when the respective currents in the active and return electrical wires are substantially equal, i.e., when neither the active nor the return electrical wire is damaged. The transformer core is further configured such that it produces a substantially larger impedance when the respective currents in the active and return electrical wires are not substantially equal, i.e., when one or both of these wires has been damaged or broken, thereby reducing the level of current passing through the apparatus to a level that does not pose a significant risk to the welfare of the patient. However, the Crow apparatus does not appear to be practical in many medical applications due to the fact that the transformer core must be relatively large in size to produce the magnitude of impedance required to reduce the current level through the apparatus to the degree required to protect the patient, thereby preventing the Crow apparatus from being incorporated into many small electrical instruments. Furthermore, the Crow apparatus continues to deliver reduced levels of current to the patient even after the return wire has been damaged. It is believed to be preferable to provide an apparatus that ceases the delivery of all electrical energy in the event that one or more of the return electrical wires is damaged or broken.